Facebook drove 21.25 percent of social referral visitors last month, up from 15.44 percent in December 2013. Twitter, meanwhile, was responsible for just 1.14 percent of social referral traffic in March, up just 0.02 percentage points since December.

Pinterest’s share of referrals last month was almost seven times that of Twitter (7.10 percent, up from 4.79 percent in December) and Twitter faces a bigger challenge from Stumbleupon (0.99 percent, up from 0.86 percent) than it is imposing on Pinterest or Facebook.

And in the race for the wooden spoon, Google+ (0.08 percent, up from 0.05 percent) is barely holding off LinkedIn (0.04 percent, down from 0.05 percent).